1. Field of the Invention
This invention relates to processes for making articles from the zein, a protein derived from corn. This invention specifically relates to a method for producing a zein article that is resistant to solvents that normally dissolve zein in a single step using melt processing.
2. Background of the Invention
Zein is a naturally occurring protein, which can potentially be obtained as a co-product of the bio-ethanol industry. Compared to most proteins, zein is characterized by a relative deficiency of hydrophilic groups. In zein, the high proportion of non-polar side chains accounts for the solubility of zein in organic solvents (such as 80% Ethanol/water) and its classification as a prolamine. Zein has been shown to be readily soluble in solvents such as dimethyl formamide (A. Biswas et. al., ACS Symposium Series, 900, Polymer Biocatalysis and Biomaterials, 141-148) and acetic acid (AcOH) (D. Sessa et. al., J. Applied Polymer Science, 105 (5) 2877-2883; G. Selling et. al., Cereal Chemistry, 84 (3) 265-270 and G. Selling et. al., Macrolmolecular Chemistry and Physics, 208 (9) 1002-1010). In order to reduce the impact solvent has on zein articles, it has been treated with cross-linking reagents such as formaldehyde either before or during the coagulation of the article by using an acid/inorganic salt bath. Additional formaldehyde treatments may be employed. C. B. Croston et al., describe such a process in Industrial and Engineering Chemistry, 37 (12) (1945) 1194-1198. Croston et al. call for zein solutions for spinning containing approximately 13 to 16.5% solids, in the pH range of 11.3 to 12.7. E. T. Cline describes another method for producing zein fibers from basic zein solutions in U.S. Pat. No. 2,475,879. Multiple formaldehyde treatments of a zein obtain from a basic zein solution are described in producing a zein fiber by C. D. Evans and C. B. Croston in Textile Research Journal, 19, (1949) 202-211. However, in each of these cases, the zein has been dissolved in solution before treatment with a cross-linking reagent such as formaldehyde.
Recently W. Uy, U.S. Pat. No. 5,750,064, has described a non-basic zein solution which can be dry spun and after post-treatment with formaldehyde gives a resilient article. The articles from these processes have reduced solubility in most of the standard zein solvents. The solids disclosed were 40-60% and required multiple steps.
W. Uy has described the use of zein and water at high temperatures in an extruder to produce fibers. After extrusion, the fibers are stabilized by passing them through a formaldehyde containing bath to give articles with reduced solubility (U.S. Pat. No. 5,580,499). However, the % solids described in this technique is very low which would limit the productivity of the process. In addition the process described is a multi-step process.
T. McMeekin et. al. describes the production of zein fibers by extruding a mixture of approximately 55-62% zein, with the remainder water, through an extruder having a die with holes of the desired diameter. The resulting fibers were then post-treated with formaldehyde by passing through a bath(s) having suitable reagents. In this process, the maximum zein concentration is 62% and the process requires multiple chemical treatments where the first step is mixing with water followed by multiple ‘hardening’ steps through treatment with formaldehyde.